Diagnostic Imaging - Ultrasound Flashcards Preview

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Flashcards in Diagnostic Imaging - Ultrasound Deck (106)
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1
Q

what type of waves does diagnostic ultrasound use?

A

high frequency sound waves

2
Q

what are the frequencies typically used in diagnostic ultrasound?

A

2-18 MHz

3
Q

what level of Hz is audible sound?

A

20-20,000 Hz

4
Q

how do sound waves and x rays differ?

A

sound waves need a material to travel through

5
Q

why are soundwaves unable to move through a vacuum?

A

rely on compression and relaxation of the medium that they are traveling through

6
Q

what does the velocity of a soundwave depend on?

A

the material it is traveling through - higher density will lead to higher velocity

7
Q

what effect is relied upon to produce ultrasound?

A

piezoelectric effect

8
Q

how does the piezoelectric effect work?

A

electrical voltage is applied to a disc within a transducer
the disc expands or contracts due to electrical current
movement is proportional to voltage and gives rise to sound wave

9
Q

what is the piezoelectric effect?

A

conversion of kinetic energy to sound energy

10
Q

what are the 2 types of disc used in production of ultrasound?

A

PZT

PVDF

11
Q

what does PZT stand for?

A

lead ziconate titanate

12
Q

what does PVDF stand for?

A

polyvinylidine difluoride

13
Q

describe how ultrasound is produced

A

voltage applied across crystal
crystal deforms due to its piezoelectric properties
leads to emission of high frequency sound waves

14
Q

is production of ultrasound in the transducer continuous?

A

no - transducer sends out a pulse of sound

15
Q

how long is the pulse of sound emitted by the the transmitter usually?

A

typically 3 wavelengths - 1.5 mm

3 compressions and relaxations

16
Q

what happens between pulses of ultrasound?

A

scanner waits for echos from tissues

17
Q

what percentage of the time it is being used it the transducer producing ultrasound?

A

1% of the time

18
Q

what percentage of the time it is being used it the transducer receiving ultrasound?

A

99%

19
Q

how is the ultrasound signal received and an image produced?

A

sound wave returns from tissues to transducer
pressure of sound waves distorts disc and so piezoelectric crystal
generates a voltage proportional to pressure
voltage is then processed by the machine and displayed

20
Q

describe the piezoelectric effect

A
voltage 
deforms piezoelectric disc in transducer
pulse of sound into tissue
hits tissue interface
reflection from tissue interface
returning echo of sound
deforms piezoelectric disc in transducer
voltage
21
Q

define acoustic impedance

A

density of tissue x speed of sound in tissue

22
Q

what has the most effect on acoustic impedance?

A

density of tissues

23
Q

how do tissues vary?

A

in acoustic impedance

24
Q

what happens when a sound crosses a boundary between tissues of different acoustic impedance?

A

some is reflected back to transducer

25
Q

what does the proportion of reflected sound depend on?

A

difference in acoustic impedance of tissues

26
Q

how much reflection of ultrasound is seen at soft tissue boundaries?

A

relatively little (e.g. fat / kidney interface)

27
Q

how much reflection of ultrasound is seen at interface between soft tissue and bone?

A

much larger percentage - bone surface will appear very bright

28
Q

when does specular (mirror) reflection occur?

A

when ultrasound beam hits a large smooth surface (e.g. small intestine wall)

29
Q

when does non-specular reflection occur?

A

beam hits small structures which have density variations

the beam is re-radiated in all directions leading to weak echoes

30
Q

what is enabled by non-specular reflection?

A

texture is given to organs which allows assessment

31
Q

describe how echoes are detected

A

sound waves reflected from various acoustic interfaces within the body
the echoes deform the crystal, resulting in the production of electrical signals
electrical signals are displayed as image on screen

32
Q

what are the 3 display modes of ultrasound images?

A

A mode
B mode
M mode

33
Q

what is B display mode for ultrasound?

A

brightness

34
Q

what is M display mode for ultrasound?

A

motion

35
Q

what is A display mode for ultrasound?

A

amplitude - oldest method, only used in opthalmology

36
Q

how is the image produced in b mode?

A

images a slice thorough a patient with a line of ultrasound
beam of ultrasound scans back and forth
image is produced from lots of lines

37
Q

what does the brightness of an ultrasound image in B mode depend on?

A

amplitude of signal - stronger echo will be brighter

38
Q

what does the position of a structure on the screen depend on?

A

time for the signal to return (longer time = further depth)

39
Q

why must organs be scanned in more than one plane in B mode?

A

as it only images a slice so full impression cannot be gained from one view only

40
Q

when is M mode most commonly used?

A

cardiac work

41
Q

how is B mode utilised to aid M mode?

A

B mode image is used to position a single line - movements along this line are followed

42
Q

how is the image in M mode displayed?

A

position vs. time

43
Q

how is a trace of movement developed in M mode?

A

continuous updating

44
Q

what is being shown by the yellow line in this B mode ultrasound?

A

the area being imaged in M mode

45
Q

in what state of consciousness can an ultrasound exam be completed?

A

tolerated well fully conscious or with light sedation

deeper sedation may be required for abdominal exam

46
Q

what are the main benefits of ultrasound exam?

A

relatively quick (e.g. diagnosis of pyometra)
non-invasive
safe

47
Q

what considerations should be made when choosing the area of the body to place the transducer?

A

area of the body which overlies the region of interest, avoiding interveneing bone or (where possible) gas

48
Q

how should the area be prepared for ultrasound?

A

clip
clean the skin
apply ultrasound gel

49
Q

when cleaning the skin why may surgical spirit not be the best option?

A

may damage transducer

50
Q

what are the 2 types of arrays found in transducers?

A

phased

linear

51
Q

is on type of transducer going to work for all imaging?

A

no - need a range of frequencies and types for optimal examination

52
Q

what 3 factors can be considered when choosing transducers?

A

type
footprint
frequency

53
Q

what are the 3 types of transducer?

A

phased array
linear array
microconvex / convex

54
Q

how is the beam steered in phased array?

A

electronically

55
Q

what size footprint does a phased array have?

A

small

56
Q

why does phased array produce a triangular shaped image?

A

sound waves diverge the further into tissue they move

57
Q

how does a linear array transducer work?

A

multiple elements are triggered in groups

image is the width of the transducer as waves don’t diverge

58
Q

how are the elements on microconvex / convex transducers arranged?

A

in a curve

59
Q

what is a benefit of microconvex / convex transducers?

A

contour better with the animal

60
Q

does the wave diverge in a microconvex / convex transducer?

A

yes

61
Q

what is the key difference between microconvex and convex transducers?

A

size of footprint - larger in convex

62
Q

what are phased array transducers useful for?

A

cardiac work - sit between ribs but larger image can be produced at depth due to divergence of beam

63
Q

what is a linear array transducer useful for?

A

limbs

64
Q

describe the similarities between phased array and microconvex transducers

A

easy to manipulate
small contact area
wide field at depth

65
Q

describe the linear array transducers

A

large contact area

large field of view near skin

66
Q

why are linear array transducers useful for superficial structures?

A

large field of view near the skin

67
Q

what happens to wavelength as frequency increases?

A

wavelength decreases

68
Q

what is a benefit of shorter wavelengths?

A

better resolution as pulse length is smaller

69
Q

how does shorter pulse length lead to better resolution?

A

better separation between structures as there is no overlap of reflections that can be seen with longer wavelengths

70
Q

what frequencies of ultrasound give good image resolution?

A

7.5-18 mHz

71
Q

what is the cost of using high frequency ultrasound?

A

sound attenuation is proportional to frequency so sound will not penetrate as far into the body

72
Q

what can high frequency ultrasound be used to image?

A

superficial structures in larger animals (e.g. eyes, tendons)

73
Q

what can low frequency ultrasound be used to image?

A
deeper structures (e.g. the liver in large dogs)
large animals (e.g. horses)
74
Q

what is the resolution like of lower frequency ultrasound transducers?

A

poor

75
Q

what cna be imaged with lower frequency ultrasound transducers?

A

deeper structures

76
Q

what range are lower frequency transducers?

A

2.5 - 5 MHz

77
Q

when should patients be starved overnight for ultrasound?

A

abdominal ultrasound

78
Q

why should patients be starved for abdominal ultrasound?

A

empty stomach is prefurrable
improves ability to examine organs
can safely sedate or GA if needed

79
Q

what is essential when performing ultrasound?

A

good contact with skin

still patient

80
Q

how can good contact with the skin during ultrasound be achieved?

A

clipping
surgical spirit
coupling gel

81
Q

what are the issues with using surgical spirit alongside coupling gel?

A

can damage transducer

82
Q

describe clipping required for an abdominal ultrasound

A

xiphisternum to pubis
line of costal arch up to lumbar muscles
include last 2-3 intercostal spaces

83
Q

describe the clipping site for heart ultrasound

A

right side
(and left for full echo)
4th to 6th intercostal space
costochondral junction to sternum

84
Q

where can the 4th to 6th intercostal space be located?

A

just behind elbow

85
Q

describe clipping sites for left kidney

A

behind last rib

below lumbar muscles

86
Q

describe clipping site for right kidney

A

include last 2-3 intercostal spaces

below lumbar muscle

87
Q

what is involved in ultrasound machine care?

A

regular cleaning of transducers and key board
removal of gel and hair after each use
safe storage of transducers and leads
regular servicing of machine

88
Q

what should be kept on record regarding ultrasound?

A

patients and areas imaged

89
Q

how may a permanent record of ultrasound findings be kept?

A

digital archive
thermal printer
video

90
Q

what does the appearance of tissues on ultrasound relate to?

A

echogenicity

91
Q

how does fluid appear on ultrasound?

A

black - anechnoic

92
Q

what does anechoic mean?

A

no echoes produced

93
Q

how does fat appear on ultrasound?

A

white - echgenic

94
Q

how to soft tissues appear on ultrasound?

A

variable - hyper/hypoechoic relative to surrounding structures

95
Q

how does a soft tissue / gas interface appear on ultrasound?

A

total reflection of sound

cannot see beyond gas

96
Q

is it possible to ultrasound through bone?

A

no - sound is reflected or absorbed

97
Q

what part of bone can be examined through ultrasound?

A

surface

98
Q

what are the advantages of ultrasound?

A
widely available
safe for operator and patient
relatively quick
non-invasive (except biopsy)
rarely need GA
sedation is optional but can be helpful
99
Q

what clinical information can be gained from ultrasound?

A

good soft tissue detail
functional information / movement
can guide aspirates / biopsies

100
Q

what is routine ultrasound used for?

A

pregnancy diagnosis and monitoring

101
Q

what is difficult to predict with pregnancy monitoring ultrasound?

A

number of foetuses

102
Q

when can ultrasound reliably detect pregnancy in dogs?

A

28 days

103
Q

when can ultrasound reliably detect pregnancy in cats?

A

20 days

104
Q

what are the disadvantages of ultrasound?

A

equipment relatively expensive and easily damaged
need to clip hair (issue in show animals)
need experience ot interpret images

105
Q

what are the issues with clinical information gained from ultrasound?

A

gas/fat/bone hinders exam

many findings are non-specific so biopsy is needed for diagnosis

106
Q

what may hinder ultrasound of the heart?

A

panting so lots of air in lungs

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